401k vs Roth 401k Calculator
Compare how a traditional 401k and a Roth 401k may grow over time based on your age, salary, contribution rate, taxes, match, and expected return. This calculator estimates both ending balances and projected after-tax retirement value so you can make a more confident savings decision.
How to use a 401k vs Roth 401k calculator
A 401k vs Roth 401k calculator helps you answer a classic retirement planning question: should you take your tax break now with a traditional 401k, or pay taxes today and potentially take tax-free qualified withdrawals later with a Roth 401k? The answer is not always obvious, because the best choice depends on your current tax bracket, your expected tax rate in retirement, your savings horizon, your employer match, and how consistently you invest.
The calculator above is designed to make that comparison practical. You enter your current age, retirement age, salary, contribution rate, current account balance, estimated annual return, salary growth, and tax assumptions. It then projects annual contributions and compound growth until retirement. It also goes one step further and estimates the after-tax retirement value of each strategy. That matters because a traditional 401k balance is not fully yours on an after-tax basis. Taxes are generally due when funds are withdrawn, while qualified Roth 401k withdrawals are generally tax-free.
What the calculator is comparing
- Traditional 401k: contributions reduce taxable income today, so you receive a current-year tax benefit. In retirement, withdrawals are generally taxed as ordinary income.
- Roth 401k: contributions are made with after-tax dollars, so there is no immediate tax deduction. In exchange, qualified withdrawals in retirement are generally tax-free.
- Employer match: employer contributions are generally made on a pre-tax basis even when your own contribution goes into a Roth 401k. That means the matched amount may still be taxable when withdrawn later.
- Tax savings side account: to keep the comparison fair, this calculator estimates that the annual tax savings from a traditional 401k are invested in a separate taxable side account. Without this step, traditional 401k results can look artificially weak.
Traditional 401k vs Roth 401k: the core difference
The easiest way to think about the decision is this: a traditional 401k gives you a tax deduction now, while a Roth 401k gives you tax-free qualified withdrawals later. Both accounts can shelter investment growth from annual taxes while the money stays inside the plan. Both are powerful retirement tools. The main distinction is timing of taxation.
If you are early in your career and your earnings are likely to rise significantly over time, a Roth 401k may be compelling because you may be in a relatively low tax bracket today. Paying taxes at a lower rate now can be preferable to paying them later at a potentially higher rate. On the other hand, if you are in a peak earning period and expect lower taxable income after retirement, the immediate deduction from a traditional 401k may be more valuable.
Quick comparison table
| Feature | Traditional 401k | Roth 401k |
|---|---|---|
| Contribution tax treatment | Usually pre-tax | After-tax |
| Current tax deduction | Yes, in most cases | No |
| Qualified withdrawals in retirement | Generally taxable | Generally tax-free |
| Best fit for many savers when | Current tax rate is higher than expected retirement tax rate | Current tax rate is lower than expected retirement tax rate |
| Employer match | Often pre-tax employer money | Employee contribution can be Roth, but employer money is typically still taxable later |
Real contribution limits and planning statistics
Good calculators should be grounded in real rules and real participation data. For 2024, the employee elective deferral limit for many workplace retirement plans, including 401k plans, is $23,000, with an additional $7,500 catch-up contribution allowed for many workers age 50 or older, according to the Internal Revenue Service. That means high earners and aggressive savers can shelter a meaningful amount each year if they prioritize retirement savings.
Behavior also matters. According to broad plan data from large retirement recordkeepers and public retirement research, workers who save earlier and increase contributions over time tend to build significantly larger balances than workers who delay. Compound growth is powerful, but only if you give it enough time.
| Retirement planning datapoint | Recent figure | Why it matters |
|---|---|---|
| 401k employee contribution limit for 2024 | $23,000 | Caps how much most workers can defer from salary each year |
| Age 50+ catch-up contribution for 2024 | $7,500 | Allows older workers to accelerate retirement savings |
| Common rule-of-thumb savings rate target | 10% to 15% of pay including match | Often used as a baseline for long-term retirement adequacy planning |
| Typical long-run diversified stock-heavy portfolio assumption | Often modeled around 6% to 8% nominal return | Shows how sensitive retirement projections are to return assumptions |
When a traditional 401k may be better
A traditional 401k may make more sense if you are in a high marginal tax bracket today and expect a lower effective tax rate in retirement. For example, a worker in their peak earning years may receive meaningful value from the immediate deduction. That tax savings can improve cash flow, support additional investing, or simply make it easier to contribute a larger percentage of salary. If those tax savings are invested rather than spent, the traditional option can be more competitive than many people assume.
- You expect lower taxable income after you stop working.
- You want the immediate tax deduction to free up cash flow.
- You are already in one of your highest expected earning years.
- You plan to relocate to a lower-tax state in retirement.
- You are disciplined enough to invest the annual tax savings rather than spend them.
When a Roth 401k may be better
A Roth 401k is often especially appealing for younger workers, workers with lower current taxable income, and people who believe tax rates may rise over time. It can also be useful for savers who want more tax diversification in retirement. Because qualified Roth withdrawals are generally tax-free, the account can provide flexibility later when managing taxable income, Medicare premium thresholds, or Social Security taxation.
- You expect to be in the same or a higher tax bracket in retirement.
- You are early in your career and earnings may rise substantially.
- You value tax-free qualified withdrawals later.
- You want to diversify your future tax exposure.
- You prefer the simplicity of not tracking whether you invested traditional tax savings separately.
How the calculator works behind the scenes
The calculator projects your salary forward each year using your salary growth assumption. It then estimates your employee contribution as a percentage of salary and adds employer match as another percentage of salary. Both the traditional and Roth paths receive the same investment return assumption and the same employer match. The difference is in taxes:
- For the traditional 401k, your employee contribution is assumed to reduce current taxable income. The tax savings are estimated by multiplying the employee contribution by your current tax rate.
- Those tax savings are then assumed to be invested in a separate taxable side account at the taxable return rate you enter.
- At retirement, the traditional 401k balance is discounted by your estimated retirement tax rate to produce an estimated after-tax value.
- The taxable side account is added to that amount to create a more apples-to-apples comparison.
- For the Roth 401k, employee contributions are after-tax, so no current deduction is modeled. The employee Roth balance is treated as tax-free at retirement, while employer match dollars are still estimated as taxable later.
This is still a planning estimate, not a tax return. Real-world outcomes depend on annual IRS limits, plan rules, vesting schedules, actual investment performance, state taxes, income changes, and how withdrawals are managed. But as a strategic decision tool, it is extremely useful.
Common mistakes people make when comparing 401k types
1. Looking only at the ending account balance
The biggest mistake is comparing balances without considering taxes. A traditional 401k balance may look larger, but a portion belongs to future taxes. A Roth 401k may look smaller on paper if the same contribution percentage is used, yet the qualified withdrawal value can be stronger after taxes.
2. Ignoring the value of the traditional tax deduction
Another common mistake is overlooking the current tax savings created by a traditional contribution. If you save 24% in taxes on each dollar deferred and actually invest that difference, the traditional option can remain highly competitive.
3. Assuming tax rates will definitely be lower later
Some savers automatically assume retirement means a lower tax bracket. That may be true, but not always. Pensions, Social Security, required distributions, part-time income, and taxable investments can keep retirement income higher than expected.
4. Forgetting about tax diversification
Often the best answer is not exclusively traditional or exclusively Roth. Splitting contributions can create flexibility later. A mix of pre-tax and Roth assets can give you more control over taxable income during retirement withdrawals.
Who should consider using both a traditional 401k and a Roth 401k?
Many plans let workers divide contributions between traditional and Roth sources. That can be a smart middle-ground strategy for households with uncertain future income, changing tax exposure, or a desire for flexibility. If you are not sure where tax rates will be decades from now, diversification across tax buckets may be more valuable than trying to make a perfect all-or-nothing guess today.
For example, someone might contribute enough to get the full employer match, then direct part of remaining contributions to Roth and part to traditional. This approach can reduce regret risk because future withdrawals can potentially be sourced from whichever account type is most advantageous for that year.
How to interpret your calculator results
When you review the output, focus on three figures:
- Total traditional 401k balance at retirement
- Total Roth 401k balance at retirement
- Estimated after-tax retirement value for each option
If the traditional after-tax total is higher, your assumptions favor taking the tax break now. If the Roth after-tax total is higher, your assumptions favor paying tax now. If the values are close, that often signals that either choice is reasonable and other factors such as flexibility, estate planning preferences, and future tax uncertainty may matter more.
Authoritative sources for 401k and Roth 401k planning
IRS 401k Resource Guide
IRS contribution limit announcements
U.S. SEC Investor.gov retirement saving guidance
Bottom line
A 401k vs Roth 401k calculator is valuable because it turns a complex tax and retirement planning decision into a measurable comparison. Traditional 401k contributions can be powerful when your current tax rate is high and your retirement tax rate is lower. Roth 401k contributions can be powerful when you want tax-free qualified income later or expect tax rates to be similar or higher in retirement. The better choice depends on your assumptions, and that is exactly why running the numbers matters.
If you want a practical rule, start with this: always capture the full employer match if available, then compare traditional and Roth outcomes using realistic assumptions. If one option wins clearly in your scenario, you have direction. If the results are close, consider using both to create tax diversification and greater retirement flexibility.